No, it doesn't -- looking at the website that's an explicit trade-off of pure performance vs 'Elixir-ish-ness'. It would certainly break a lot of expectations to have data mutating like that without it being hidden away somewhere, so I can understand why they went that way.

In my case the data I'm dealing with is more of a store than a single data item, so I'm leaning on the example of things like ETS. Also it's within a single application rather than being a large generally-available library, so the trade-offs are different. It would be interesting to know if they did tests though.

Probably not ideal since Polars builds on Apache Arrow and that tends to want to treat the structure as immutable if I recall correctly.